1. Field of the Invention
The present invention relates to an electronic musical instrument adapted for digital control of the temperament of note frequencies and a transposition operation.
2. Description of the Prior Art
Heretofore, note frequencies of electronic musical instruments have been set on the basis of a temperament called an equal temperament. With the equal temperament, musical intervals are each formed by one of 12 "semitones" of the same frequency ratio into which an "octave" having a frequency ratio of 1:2 is divided equally.
As a method of obtaining note frequencies of the equal temperament, there has been well known, for example, a so-called "top octave" system according to which 12 standard toned are generated by dividing a sufficiently high main clock frequency into frequencies which approximately form musical intervals of the equal temperament and then octave relations are generated by the use of a plurality of 1/2 frequency dividers.
On the other hand, since classical musical instruments of the Baroque era, in particular, employed such classical temperaments as a pure temperament, a Pythagorean temperament, a meantone temperament and so forth, there have also been proposed methods of generating note frequencies of such classical temperaments for electronic musical instruments. For instance, 12 standard tones of the pure temperament are produced by frequency dividers of frequency dividing ratios corresponding to the musical intervals of the pure temperament and then octave relations are produced by the same frequency division as in the "top octave" system. Further, there has been proposed a standard 12-tone generator including a complex combination of 1/2 and 1/3 frequency dividers, noting that the Pythagorean temperament uses, as standard tones, purely perfect fifths having a frequency ratio of 3:2.
With these conventional electronic musical instruments, however, the temperament used is determined through the use of a complex circuit arrangement, and for switching the temperament, for example, between the pure and the equal temperament, individual temperament generators are needed; namely, they are defective in that the temperament system cannot easily be changed and that the circuit arrangement is enormous.
Moreover, even if such electronic musical instruments are equipped with a transposition function, musical intervals relative to the transposed fundamental tone, in the classical temperaments, do not become equal to musical intervals having respective tones moved in parallel as in the equal temperament. To prevent this, a master clock frequency must be varied in accordance with the transposition, but it is difficult technically to change the sufficiently high master clock frequency stably and accurately for generating 12 tones. Therefore, they possess such a serious drawback that satisfactory accuracy of frequency and stability cannot be obtained.